The present invention relates to inflatable seat belt devices provided with air belts. Air belts typically include an inflatable bag which may be inflated by gas produced in emergencies such as a vehicle collision. In particular, the present invention relates to an air belt for an inflatable seat belt device including at least a cover for covering a mesh webbing which expands together with the bag expanding with gas.
Conventional seat belt devices comprising webbing are generally installed in vehicles such as automobiles in emergencies such as a vehicle collision, thereby protecting the passengers from being injured due to the collision.
However, in such seat belt devices, since the width of the webbing for restraining the passengers may is relatively small, the passengers may receive relatively large loads.
Therefore, an inflatable seat belt device which includes an air belt has been proposed in, for example, Japanese Patent Application Publication No. 6-135293 (incorporated by reference herein), in which webbing is formed into a bag and shaped as a belt in order to serve as a general seat belt when not inflated. The bag-shaped webbing is inflated by introducing gas ejected by gas generating means into the bag-shaped webbing in an emergency. The inflated bag-shaped webbing receives the passenger. By using such an air belt for the inflatable seat belt device, the kinetic energy of the passenger is distributed over a larger area, thereby dispersing the load, whereby the load applied to the passenger becomes relatively small and the passenger is protected more effectively.
The webbing becomes shorter in the longitudinal direction and the thickness is increased when the webbing is inflated. As a result, the webbing presses against the passenger""s body due to the increased thickness. Furthermore, the same effect as winding the webbing can be achieved. The inflating webbing provides an initial retaining force similar to that of a pretensioner.
Generally, the air belt disclosed in the above publication or an air belt 1 used in the inflatable seat belt device shown, for example, in FIGS. 5(a) and 5(b) includes bag-shaped webbing 2xe2x80x2, a tube 3xe2x80x2 which is made of an elastic material, such as urethane or silicone, capable of being formed relatively thin and having heat-resistance and relatively high strength and which is inserted into the webbing 2xe2x80x2, and a tube-like cover 4 for covering the webbing 2xe2x80x2 which is made of a resin, such as polyester.
The tube-like cover 4 is formed such that right and left hems 4a and 4b of a rectangular cloth overlapping each other are sewed on each other by a sewing thread 5a. In this case, the right and left hems 4a and 4b of the cloth are each folded toward the inside of the tube-shaped cloth and the folded parts are sewed together by the sewing thread 5a. Therefore, a sewed part 5 is positioned inside the tube-shaped cloth.
In the air belt 1 formed as described above, the webbing 2xe2x80x2 expands when the tube 3xe2x80x2 expands with gas introduced from an inflator (not shown). In this case, the sewing thread 5a of the sewed part 5 of the cover 4 breaks due to the expansive force of the webbing 2xe2x80x2. As a result, the cover 4 extends, and the webbing 2xe2x80x2 and the tube 3xe2x80x2 expand further.
However, because the cover 4 is provided with the right and left hems 4a and 4b which are folded at the sewed part 5, the thickness of the cover 4 is greater at the sewed part 5 than at the other parts of the cover 4. The thickness of the cover 4 is uneven in the width direction of the cover 4, thereby providing an uncomfortable sensation to the passenger using the seat belt.
The bending strength of the cover 4 in a direction perpendicular to the longitudinal direction of the belt increases due to the fold and sewing of the cloth. The bending strength differs between the hem 4c and a hem 4d opposite to the sewn part 5, thereby also providing the passenger with an uncomfortable sensation when applying or using the seat belt.
Moreover, when the air belt 1 passes through a guide hole of a belt guide for guiding the air belt 1 toward a passenger (an intermediate guide such as disclosed in the above-referenced publication), a problem occurs because it is difficult for the air belt 1 to smoothly slide through the guide hole because of the increased bending strength of the cover 4.
Accordingly, an object of the present invention is to provide an air belt for an inflatable seat belt device, which can be formed so that the thickness of the air belt is uniform in the width direction and the bending strength of the air belt is substantially the same between at the right hem and at the left hem of the air belt.
Another object of the present invention is to provide an air belt for an inflatable seat belt device, which includes a cover of which the bending strength is reduced to a lowest possible level, whereby the air belt can smoothly slide through a guide hole of a belt guide.
Therefore, an air belt for an inflatable seat belt device is provided according to the present invention. The air belt comprises a bag capable of expanding when gas is introduced into the bag; mesh webbing receiving the bag and capable of expanding according to the expansion of the bag; and a tube-like cover for covering the mesh webbing. The cover is formed with cloth which is woven with warp yarn and weft yarn and is formed into a tube by tangling and connecting the weft yarn at hems of the cloth with an entanglement-thread. The entanglement-thread breaks due to an expansive force produced when the mesh webbing expands, whereby the cover extends so that the mesh webbing expands further.
According to the present invention, a small-denier-warp region may be formed in a predetermined region of the belt. The small-denier-warp region may be on at least one side of the part of the cover that includes the entanglement-thread. The part of the cover that includes the entanglement-thread is formed by tangling the weft yarn with the entanglement thread. The small-denier-warp region being provided with a warp yarn having a denier smaller than that of the warp yarn disposed in a region other than the predetermined region.
When the mesh webbing of the air belt used in the inflatable seat belt according to the present invention expands according to the expansion of the bag by the gas supplied from the gas generating means in an emergency, the entanglement-thread of the tube-like cover breaks due to the expansive force.
The cover extends widely and the mesh webbing and the bag thereby fully expand quickly. The kinetic energy of the passenger is distributed over a larger area, thereby dispersing the load. As a result, the load applied to the passenger becomes relatively small and the passenger is protected more effectively, than in the case of the known air belt.
The cover is formed into a tube by tangling and connecting the weft yarn with the entanglement-thread. Therefore, the sewn part that increases the thickness and the bending strength provided in the known air belt can be eliminated.
The thickness of the cover of the air belt becomes more uniform in the width direction and the bending strength of the cover becomes substantially uniform between the right and left hems, thereby suppressing the uncomfortable sensation of the passenger and improving sensation during the usage of the belt.
Since the thickness and the bending strength of the cover are reduced by eliminating the sewn part, the air belt 1 can smoothly slide through the guide hole of the belt guide, and the belt can be wound and unwound smoothly. In particular, the air belt can be wound directly to a retractor because the thickness of the cover is reduced.
According to the present invention, the small-denier-warp region xcex1 may be provided in a predetermined region on at least one side of the entangled-connected part which is formed by tangling the weft yarn with the entanglement-thread. The cover of the air belt provides a soft sensation at a hem of the cover at the side of the entangled-connected part. Therefore, the passenger touches the hem of the cover with a comfortable soft sensation when the passenger applies the air belt in an ordinary seat belt state, thereby suppressing the uncomfortable sensation of the passenger and improving sensation during the usage of the belt.
According to the present invention, heat-fusion yarn may be used as at least one of the warp yarn and the weft yarn. With this arrangement, the heatfusion yarn adheres to the adjacent yarn when it melts, whereby the adjacent yarns and the yarns crossing each other adhere to each other, and the ravels of the yarn are not produced. In particular, when the heat-fusion yarn is used as the weft yarn and the warp yarn, the displacement of the warp yarn can be avoided. Displacement of the warp yarn is produced when the air belt in an ordinary non-expanded state is wound or unwound and slides on a belt guide which guides the air belt.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed.